CHAPTER OF CRITICISM. 215 



thing of my own — that is another affair ; if I am enabled to please*, as you are 

 kind enough to think I do, I am satisfied. You do wisely in reporting the Trans- 

 actions of the London societies ; it will be advantageous in many ways. The 

 " Chapter of Miscellanies " is another department that I trust, and am indeed 

 sure, you will find it your interest to keep up. 



Yours, very sincerely, 



Edwin Lees. 



CHAPTER OF CRITICISM. 



Some Observations on Ananchites and Spatangus. 

 To the Editor of the Naturalist. 



London, May 17, 1837. 



Sir, — In the last number of The Naturalist (p. 101), I observe a slight error 

 occurring in an extract from Karsten's Archiv. fur Mineralogie, relating to the 

 singular appearance sometimes presented by the casts of Echinites, owing to the 

 existence of crystals of calcareous spar upon the interior of the original shell. 

 The translator has made use of the word blade instead of plate, by which latter 

 term the polygonal portions composing the external skeleton of the Echinus are 

 designated. The phenomenon referred to in the work above quoted, and which 

 the writer has explained by the examination of two fossils in the Royal 

 Mineralogical Museum of Berlin, is an extremely puzzling one to those who may 

 meet with a " Honey-comb Echinus," and are ignorant of the mould upon 

 which the cells are formed. I am not aware that any solution of the problem has 

 been published elsewhere, although the phenomenon itself, and the manner in 

 which it has been produced, must be familiar to those who have made this 

 interesting class of fossil bodies an object of investigation. 



Fossil Echinites having crystals of carbonate of lime deposited upon their 

 internal surface, although by no means of common occurrence, are found in all 

 chalk districts which furnish the remains of Radiata in abundance. I have 

 never seen these crystals lining the entire surface ; about half or a third only 

 being thus occupied, and usually confined to the spherical portion of the shell. 

 It is a curious fact also, that (so far as my own observation has gone) this 

 peculiarity is only exhibited by the genera Spatangus and Ananchytes. 



* The papers of our valued correspondent are always sure not only to be interesting to all 

 classes of readers, but also to contain much original information to attract the attention of the 

 scientific naturalist Ed. 



